For a wide variety of applications, chairs are nowadays provided with features which provide enhanced comfort to the person using the chair. For illustration, office-type chairs are commonly utilized in modern working environments to provide an occupant with a level of comfort while performing certain tasks that require a person to be in a seated position for an extended period of time. Such chairs may include a chair back height adjustment mechanism which allows a height of the chair back to be adjusted.
The chair back height adjustment mechanism may have a guide and an adjusting device which is moveably supported thereon. The guide may be shaped as a so-called J-bar, for example, which extends upward at a rear side of the seat. An adjusting device acts as backrest carrier and is moveably supported on the guide. The height of the chair back may be adjusted by adjusting the position of the adjusting device on the guide.
An example for a height adjustment mechanism having such a configuration is described in U.S. Pat. No. 7,275,790 B2, for example.
In this type of chair back height adjustment mechanisms, the guide has a high strength or is attached to a separate carrier which has high strength, so as to support the forces acting onto the chair back. To this end, the guide may be formed from or may comprise a steel bar, for example. It is challenging to manufacture a combination of guide and adjusting device such that the inner dimensions of the adjusting device match the outer dimensions of the guide, at least in a lateral, i.e. left-right, direction. Reducing the manufacturing tolerances for the high strength part of the guide would address this problem, but would significantly add to the complexity of the manufacturing process and, thus, manufacturing costs. The adjusting device may be provided with an oversized inner cavity which is sufficiently large to allow the guide to pass therethrough, taking into consideration the manufacturing tolerances for the guide. This may give rise to a wobble of the adjusting device on the guide, which in turn gives rise to a wobble of the chair back. Such a wobble or play is generally undesired.